In the manufacturing of certain ceramic objects, higher density and improved properties may be achieved when a low density preform of the object is consolidated by hot isostatic pressing (HIP) processing. For some ceramic materials to be processed this way requires that the object be hermetically encapsulated. This encapsulation prevents the gas used during HIP processing from infiltrating the preform and defeating consolidation. A simple shaped object is placed in a glass enclosure, the enclosure is evacuated, and sealed to provide the encapsulation prior to processing in the pressure vessel. In the course of the HIP process, the glass enclosure softens and collapses into close contact with the preform. The resulting soft glass forms a hermetic membrane that allows densifying pressure to be applied to the surface of the preform for consolidation.
The disadvantages of the standard procedure are that the enclosures have to be specially formed to the approximate shape of the preform, sealed around the preform, and then evacuated through a nipple that is sealed when the evacuation is complete. At best, this procedure requires the purchase of specially formed glass parts and sealing machinery, and at worst, it requires the services of a glass blower for each individual preform.
Representative prior art proposed by Adlerborn in U.S. Pat. No. 4,081,272 describes a technique in which a preformed ceramic shape embedded in quartz powder is evacuated and sealed inside a glass capsule prior to isostatic processing.
Besides the aforementioned Adlerborn U.S. Pat. No. 4,081,272, the prior art in the field includes: Adlerborn U.S. Pat. No. 4,455,272 which describes the processing of a preform encapsulated in an evacuated glass capsule; Wolfe et al U.S. Pat. No. 4,462,816 which teaches collapsing an open glass tube around several spaced preforms in a vacuum, and cutting the collapsed tube into individual encapsulations to process; Goldstein U.S. Pat. No. 4,722,825 in which a ceramic-lined metal tube is produced by sintering a metal/ceramic preform in an evacuated glass capsule under atmospheric pressure; and Kobe Steel Japanese Pat. No. 54-35806 which shows isostatic processing; in a sealed but unevacuated metal or glass container, of a metal or ceramic capable of absorbing the residual O.sub.2 and N.sub.2 in the container.